The present invention relates to the field of tape measures and more particularly to locks used to prevent retraction of the retractable tapes used in tape measures.
A tape measure typically includes a case, a metal tape retractably mounted within the case, a retraction means for retracting the tape, a stop for preventing the end of the tape from retracting into the case, a clip to attach the tape measure to clothing, such as a belt, and a lock which releasably secures the tape in an extended position. A common prior art lock includes a toggle switch and a lock shoe attached to the toggle switch, such that when one end of the toggle is depressed, the lock shoe is moved against the tape which is in turn forced against the inside bottom of the case. Pushing the other end of the toggle releases the lock shoe, allowing the tape to freely retract into the case.
Prior art tape measures employ lock shoes in several configurations. In one such configuration, the lock shoe is a substantially straight finger, which is connected to the toggle by a radial arm. The finger, or lock shoe, is held between the side of the case, which is angled inward, and the side of the tape rolled within the case. When the toggle is depressed, it swings the end of the shoe connected to the radial arm inward with respect to the side of the case, and the opposite end of the shoe is swung outward with respect to the case. Because the ends of the shoe, which is a constant length, swing through an arc, the ends travel laterally with respect to the case bottom. Thus, as the toggle is pushed into the case, the shoe tends to depress the tape against the inner case bottom, eventually wedging the tape with sufficient force to overcome the spring force tending to retract the tape into the case, thereby locking the tape in place. However, this construction requires that the case be angled outward between the toggle and case bottom to form a fulcrum for the lever of the shoe, and the toggle end of the shoe must be outside the envelope of the tape coiled in the case. The shoe engages the tape directly below the toggle pivots, and the plane intersecting the toggle pivots and the shoe adjacent the lock shoe is substantially perpendicular to the case bottom. Because the lock shoe adjacent the tape and the toggle pivot define a plane perpendicular the base, and the plane must be disposed outside the diameter of the coiled tape within the case, the case bottom must be longer than the diameter of the tape coiled within the case. Therefore, the bottom of the case must be longer than the width of the case at the fulcrum point. Therefore, in this construction the case bottom is commonly substantially longer than the coiled tape width.
In another prior art tape measure, the toggle is mounted on the front wall of the case adjacent a vertical shoe guide in the sides of the case. The sides of the shoe fit within the shoe guides in each side of the case, such that the entire shoe is restricted to vertical travel. The toggle has a curled bisected finger which forms a T-slot receptacle in which a mating T-slot on the shoe is engaged. The radius of the curl is sized to cause the shoe to move vertically in the vertical restricting shoe guides in the sides of the case as the toggle is pivoted. The toggle includes a pair of recesses in the bisected finger portion which act as lock recesses when the toggle is fully depressed to cause the lock shoe to engage the tape. Because the entire lock shoe slides vertically in the shoe guides and is located on the front of the case, the shoe must engage the tape outward the diameter of the tape coiled within the case. This limitation requires the bottom of the case to be substantially longer than the diameter of the coiled tape. In a 300-foot tape measure, the interior of the case defines a 2.75 to 3.00-inch chamber to store the retracted tape. Therefore, these tape measures are typically 3.50 inches long. U.S. Pat. No. 3,578,259 describes a lock system having this construction.
In U.S. Pat. No. 4,527,334, another lock system is disclosed, wherein the tape is attached to a circular housing, and the circular housing is in turn releasably engageable with the lock. In this configuration, the lock has an arm which releasably engages the circular housing on the perimeter of the housing. The lock incorporates a metal coiled spring to assist in biasing the lock against the housing to maintain engagement contact.
U.S. Pat. No. 4,479,617 discloses a lock wherein a reciprocating locking plate has cams which are actuated by the toggle. The toggle has a swing type radial arm which engages the cam, and the toggle motion of engaging and disengaging the toggle causes lateral motion in the locking plate. The locking plate, in turn, pinches the tape against the case bottom to lock the tape in position.
One deficiency of prior art tape measures having the shoe lock the tape against the case bottom, is that the bottom of the case must be long enough to accommodate the lock shoe and associated lateral travel of the lock shoe. Further, in certain devices, toggle and vertically restrained shoe must be located outside the coil of the tape. Therefore, the total length of the case bottom must equal the diameter of the tape plus the arc length of travel of the end of the lock shoe in response to movement induced at its other end by the toggle, or, the width of the shoe and guide wall. A prior art toggle mounting system may commonly require 1/2 inch of space which must be added to the bottom of the case.
The present invention overcomes these deficiencies of the prior art.